Abstract Book

S1012

ESTRO 37

t-test was used to assess statistically significant differences. Results KB-based plans were generally better than or equivalent to clinical plans. A summary of the results is shown in Figures 1 and 2. Similar trends could be appreciated without major differences between the three steps, apart a larger bowel sparing in step 3 of only-RPvsRA . When comparing RPvsRA , PTVs coverage and homogeneity were comparable. Concerning OARs, RP was always better with most of the improvements statistically significant. When comparing only-RPvsRA , average PTVs coverage was slightly improved and a better average sparing was obtained for OARs, although only few differences were significant. Concerning gEUD, RP was significantly better than RA : gEUD reduction >1Gy were found in 80% of pts for rectum, bladder and bowel. For only-RP vs RA, the average differences were significant only in few cases: although, gEUD reduction >1Gy was found in 50% of pts for rectum/bladder and in 70% for bowel; while a worse >1Gy performance of only-RP vs RA was found for at least one OAR in only 20% of pts.

planning situation. A robust KB-model was able to automatically generate high-quality plans; the interaction of a planner further improved planning performances. In both cases, a large reduction of the time for planning may be obtained. EP-1873 Autoplanning for VMAT accelerated partial breast irradiation L. Marrazzo 1 , C. Arilli 1 , I. Meattini 2 , M. Casati 1 , C. Talamonti 1,3 , L. Livi 2,3 , S. Pallotta 1,3 1 Azienda Ospedaliera Universitaria Careggi, Medical Radiation Physics, Firenze, Italy 2 Azienda Ospedaliera Universitaria Careggi, Radiation Oncology, Firenze, Italy 3 University of Florence, Department of Experimental- Clinical and Biomedical Sciences “Mario Serio, Florence, Italy Purpose or Objective To evaluate the plan quality of accelerated partial breast irradiation (APBI) generated by the Auto-Planning (AP) module of the Pinnacle3 (Philips Medical Systems, Fitchburg, WI) treatment planning system (TPS). AP automates the consecutive multiple sequence optimi- zation process using a progressive optimization algorithm. Material and Methods AP treatment technique (beam parameters and optimization goals) was first assessed and validated on a sample of 10 APBI cases (left quadrant). Twenty patients, who had previously been planned with Monaco (Elekta AB, Stockholm, Sweden), were then replanned using the AP module. AP was performed with no further manual intervention. Dose distributions were compared in terms of dosimetric plan parameters, degree of modulation, monitor units (MU) and treatment time, and by blind qualitative scoring by a treating physician. In order to check that both manual and AP plans could be reliably delivered, dosimetric verification was performed and evaluated in terms of γ passing rate and point dose measurements. Statistical significance of differences between AP and manual plans was evaluated using paired two-sided Wilcoxon signed-rank test. Results In Table 1, the plan parameters are reported for both manual and AP plans. A statistically significant improvement in PTV coverage (average improvement 1%; range 0-4%) and PTV dose homogeneity (average reduction in PTV V 105% 6%; range 3-26%) was observed for AP plans compared to manual.

Conclusion The suggested stepping procedure validated the possibility of KB-planning optimization in supporting/ partly replacing manual optimization in a complex